Process for producing ferro-leather



UNITED sTAr Es PATENT osr ce.

WrLHELM unns ive, or rnnrnnne, ennr aiiv.

PROCESS FOR 'PRODUCING FERRO-LEATEER.

No Drawing. Application filed January as, 1917, Serial No. 144,099. Renewed January 27, 1921. 7 Serial T 0 (1% whom it may concern Be it known that I, WILHELM MENSING, a subject of the King of Prussia, German Emperor, residing at'No. 5 Hainichenerstrasse,- Freiberg, Germany,

in the Kingdom of Saxony, have invented new-and useful Improvements in Processes for Producing Ferro- Leather; and I do hereby declare the "following to be a full, clear, and exact description of the same.

According to the ferri-tanning processes heretofore known it is not possible to produce, without difficulty, a tough and perfectlyr durable leather, which is proof against tearing and fracture, from ferrisalts obtalned by oxidlzing ferro-salts with chromic acid or nitrlc acid. This is due to the fact that the ferri-salt solutions have a very high dissociating capacity and therefore incline to separate insoluble ferric compounds, which are formed particularly in the outer layers of the leather and thus produce a rough brittle grain.

Attempts have been made to overcome this drawback of the ferrotanning process by using ferri-salts, but in the presence of ferro-salts, which latter prevent the formation of basic ferri-salts. Although in this case a rough brittle grain is avoided, still, owing to the mutable character of the ferro-salts,',.

the quality of'tlie leather is reduced by keeping, as is shown by the grain becoming brit- -'=tle and by the leather being more easily torn. Now it has beenfound that these drawbacks are avoided, if, in preparing the ferric solutions and tanning-liquor, as well as in the tanning process itself, care 15 taken, to

prevent the hydrolytic splittingup of the ferri-s'alt, as" far as possible, and to avoid" ferro-salts in the tanning liquor, or their formationin the leather. 7

In order to assure that contained in the tanning liquor, and topre- .vent their subsequent formation in the leather,'the tanning is carried out, according to the present invention, in the presence of an excess of oxidizing agents. Then making ferri-salt solutions from ferro-salts by oxidation with the assistance of chromic acid or nitric acid, or the like, such a quantity of this oxidizing agent is used that an excess of the same remains in a non-reducible form. 3

It has been found that it is of special advantage to use oxidizing 'chlori'd compounds nitric acid. Further a very no ferr'o-salts are free'from iron, such as sodium-chlorate,.potassium-chlorate, barium-chlorate or chloric 1 acid, instead of the usual oxidizing" agents, such aschromic acid or nitric acid. The use of such chlorate compoundsis cheaperthan chrome compounds and thefp rocess'i'is "simpler and more easily carried out'th'an with durable leather is obtained which keeps well. Y 1 I In order to obtain a perfect result, .it is necessary, as above set forth to preventa hydrolytic splitting up of the ferri-sa-lt. *fAs high temperatures exercise a decomposing Specification of Letters Patent. Patented Blair. 15,1921,

action on the ferri-salts it"is advisable, in

making the ferric solution, not to much ex ceed 35 C. and to, then rapidly cool the so- I lution down to the temperature of'the-roorn.

Because, further, dilute ferri-salt solui tions split up relativelyquickly into a basic salt and free acld, While, according as the concentration increases, this splitting up does not occur so easily, it is advisable to use strong ferri-salt solutions for tanning, thus without the usual slow improvement of the tanning liquor. Y Y

If depilated skins ready for tanning are a treated with concentrated solutions *of. a r

ferri-salt produced at a moderatetempera ture, which ferri salt is perfectly free from ferro-salt and contains a slight excess of an oxidizing agent, so that any ferro-salts which may happento be "present are oxidized, then leather of good marketable'qua h ity is obtained, which,-according to experi-- nients, after being kept for six years have as good a quality as when first made.

By observing the directions iand by suitable carrying out the-process hard or soft flexible leather can be made, ifthe' acid combined with: the ferric oxid, beginning with the most difficul-tly soluble'basic salt, is increased until a 'weakly acid salt is cbtained. a When using slightly acidor neutral ferri salts the depilated skins from which the lime has been separated are subjected to a preliminary -treatment with slightly alka line salts, such as borax,or they are firstly; tanned with aluminium or chromic oxid" salts rendered basic, so that any free acid present may be combined.

. x mp A- ferri-salt solution of about 10% Fe O vis produced either by dissolving in water whena fresh cut shows a uniform tanning some ferri-salt for instance ferric sulfate or by oxidation of a ferro-salt solution, for in stance ferrous sulfate by means of air or nitric acid. t

Care should be taken when the solution is prepared that a temperature of C.

benot exceeded anda sufficient quantity of a non-volatile oxidation agent is added that there be always present in the 10% ferric solution, 1% of that non-volatile oxidation agent in therfree state. When the ferri-salt solution is prepared by oxidation of ferrous salts by means of chromic acid, nitric acid or chloric acid, so much of the oxidizing; agent .must be added rightaway that there remains about 10%"thereof innonreduced state.

For tanning depilated skins which have. been. pickled and preliminarily tanned a suitable quantity of a;?;% solution of sodium chloridor sulfate of soda is produced, and a sufficient quantity of the ferric solution produced in themean timeis added to assure that the tann ng liquor OOHiIRlIlS at least 1 to 2% ferric oxid (Fe O whereuponthe tannin process is commenced at once without further IIIIPI'QVGIIIGIllLy It is finlshed and no further reduction ofthe strength of the liquor can be ascertained.

By suitablefinishing-processes it is possible togiveto the ferro leather made in accordance with this invention further excellent properties. H r

The ferro-leathertaken out of the tanning liquor is not washed at once, but is only liberated as far aspossible from the liquor by. pressing Orstretching, whereafter it is oiledon the grain with mineral oil alone, and on the inner side withmineral oil to which sulfurized oils have been added, and

the leather is then dried. When dry the leather can be impregnated with ceresin, paraffin or other mineral fats, for special purposes, and then washed with water.

If it is desiredto reduce the reacting property of the ferric salts contained in the leather to such an extent that vegetable tanning, or similar substances, for example cellulose extracts or neradolcan only exercise a weak action on saidferric salts, a sufiicientjquantity of a, salt of alkaline reaction is added to the waterused for the washing, and the leather is allowed to remain in this weak alkaline solution until on a fresh out no, or but little, black coloring is produced with a neutral tanning substance. Thereafter the leather is treated according to the purpose for which it is to be used.

Owing to the close character of the grain caused by the tanning and finishing process it ispossible to finish leather tanned with ferric salts on the inner or flesh side.

If the leather tanned with ferric oxid salts is treated with reducing agents, for

instance with-a 3% solution of sodium thiosulfate, if necessary after a preliminary treatment with a diluted acid solution for instance with a 5% solution ofsulfuric acid, the ferric oxid salts in the outer layers will be reduced into ferro-salts. In doing so the tanning salt is partly removed from the outer layersof the leather, and this exercises a bleaching action on the leather, producing,

at the same time, a finergrain.

What I claim and desire to secure by- Letters Patent of the United States is l. The process for'producing tough and durable leather from animal skins of all kinds which comprises treating the skins with a solution of ferri-salts in the presence of an excess of chlorates such as sodium chlorate, V

2. The process for producing tough and durable leather from animal skins of all kinds which consists in preliminarily treating the depilated decalcified skins with weak salts of alkaline reaction and then tanning said skins in a solution of ferri-salt in the presence of an excess of some oxidizing agent. V

3. The process for producing tough and durable leather, from animal skins of all' kinds which consists in tanning the skins with a solution of ferri-salts in the presence of an excess of some oxidizing agent, and in washing out the uncombined ferri-salts after in a solution of ferri-salts in the presence of anexcess of some oxidizing agent, and in then treatlng the surface of the leatherwith I reducing agents. V e v 6. The process for producing tough and durable leather from. animal skins of all kinds which consistsin tanning saidskins in asolution of ferri-salts in the presence of an excess of some oxidizing agent, in treating the surface of said skins with dilute acid solutions, and then with reducing agents.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

'WILHELM MENSING.

lVitnessesz' e l MARTA PICKEL,

CLARE SIMON. 

